The Lebanese security officials said the gunmen were killed as they tried to enter the Syrian town of Tal Kalakh, near the Lebanese border.

Syrian state-run media also reported that Lebanese gunmen were killed. But the SANA report said there 17 - not 20 - fighters.

The Lebanese gunmen were Sunni Muslims, as are the vast majority of Syria's rebels. Syrian president Bashar Assad - along with his most elite troops - belong to the Alawite sect, an offshoot of Shiite Islam.

Lebanon is particularly vulnerable to getting sucked into the conflict in Syria. The countries share a complex web of political and sectarian ties and rivalries that are easily enflamed. Lebanon, a country plagued by decades of strife, has been on edge since the uprising in Syria against Assad began in March 2011, with deadly clashes between pro- and anti-Assad Lebanese groups erupting on several occasions.

The deaths came as rebels have tried to close in on the Syrian capital, Damascus, in recent days.

On Friday, Syrian soldiers fought rebels in and around the capital as internet and most telephone lines were blacked out for a second day. But the intense battles around the country's international airport appeared to have calmed.

The airport road had reopened and the head of the Syrian Civil Aviation Agency, Ghaidaa Abdul-Latif, said the airport was operating "as usual".

A minibus driver said he heard explosions in the distance as he drove through Damascus.

He said: "There are extreme security measures in Damascus today. We were stopped at several checkpoints. Our IDs were checked and they even opened all the bags and suitcases."